The present invention relates to a new and improved construction of a load-weighing apparatus for an elevator car.
In its more particular aspects, the present invention relates specifically to a new and improved construction of a load-weighing apparatus for an elevator car and containing wire strain gauges which are interconnected to form a bridge circuit. There is also provided an amplifier circuit, the input side of which is connected to the output side of the bridge circuit. The output side of the amplifier circuit is connected to an elevator control.
Load-weighing apparatus in elevators serve the purpose of generating load-proportional signals which are required for the elevator control. In simpler designs of elevator systems it is generally sufficient to generate signals which indicate the conditions "occupied", "full load", and "overload". Beyond that and for more refined controls there are required load signals which are generated in finer steps or continuously.
This requirement can be met by using the apparatus as known, for example, from Swiss Pat. No. 425,134. Therein the elevator car platform is supported at an elevator car platform frame of the elevator car by means of springs, the deflection of which is evaluated such that load-proportional signals are generated. There is suggested, among other things, for the evaluation of the spring deflection that a measuring point is formed by means of a lever system, and that this measuring point is located at the center of the elevator car platform. The deflection travel of the measuring point is proportional to a mean deflection of all the springs. The displaceable measuring point or location can be connected, for example, to a plunger-type armature of a plunger-type coil or to a wire strain gauge, so that a continuous generation of load-proportional signals is possible. Such apparatus is relatively complicated and expensive. Furthermore, due to the inertia and insensitivity of such apparatus in the lower load range there is hardly possible a faultless signaling of small load variations.
In a text book entitled "Elektronik", second part, published by Europa-Lehrmittel, Wuppertal, 4th edition, 1978, pages 14 and 15, there is described a load-weighing apparatus of the type as initially described and in which the wire strain gauges are incorporated into a load cell. Such load cells are commercially available and are relatively expensive and therefore unsuited for use with cost-favorable elevators. Furthermore, also with this apparatus there is not readily obtained a faultless detection of small load variations in the lower range of loads.